[QE-users] ph.x Raman calculations

[Lorenzo Paulatto]

Yes, when anharmonicity get stronger, the perturbative approach of d3q eventually breaks down. It is always possible to use stochastic (sscha) or molecular dynamics methods. Each method has trade-offs, in terms of: computational cost, ability to cope with strong anharmonicity, treatment of quantum ions/very low temperatures, and last but not least in my opinion, giving an insight to the physical processes.

regards

Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ (https://link.getmailspring.com/link/6A135B8E-AE49-4ACA-A7D4-E5CDAF809154@getmailspring.com/0?redirect=http%3A%2F%2Fwww.impmc.upmc.fr%2F~paulatto%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D) - https://anharmonic.github.io/ (https://link.getmailspring.com/link/6A135B8E-AE49-4ACA-A7D4-E5CDAF809154@getmailspring.com/1?redirect=https%3A%2F%2Fanharmonic.github.io%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D)
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On Mar 31 2021, at 4:35 am, Terry Frankcombe <t.frankcombe at adfa.edu.au> wrote:
> While we are talking about interesting ways to include anharmonic
> effects, it's worth taking a look at SSCHA: http://sscha.eu/
>
> Not necessarily computationally inexpensive.
>
> On Wed, 2021-03-31 at 07:20 +0900, Kazume NISHIDATE wrote:
> > > 2021/03/31 1:00、Lorenzo Paulatto <paulatz at gmail.com>のメール:
> > >
> > > Hello you can take into account anharmonicity with the d3q code which is included in QE,
> >
> >
> > This may be the most sophisticated way to account for the
> > anharmonicity from first principle. I'm impress by the ingeniousness.
> > Thank you for your notice.
> >
> > btw-
> > The methods described in my previous message are heavily relying upon
> > a brute force manner. The only advantage of the method should be the
> > automatic inclusion of higher order terms beyond the third-order, but
> > of course its resolution, especially when it was obtained by MD, would
> > be very low.
> >
> >
> >
> >
> > best regards
> > kazume NISHIDATE
> > 敬具　西館数芽
> >
> > nisidate at iwate-u.ac.jp
> > kazume.nishidate at gmail.com
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
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